Terraria Wiki Guide

Clown

Clowns only spawn on hardmode during a blood moon. because of the nature of their attacks (throwing bombs towards the player/obstruction in their path), Clowns will pose a great threat to an unprepared player's home and NPC.

It is advisable that a player adquitely prep their homes for such an attack either by using Dungeon Brick (which is impervious to explosives), or using ores located in hardmode (Cobalt/Mythril/Adamantite) to form a layer before the outside of your home. The explosive radius of the Clown's bomb is 3x3, so the required protective layering should be about 3 blocks away from your home.